Officers are appealing for information, witnesses and dash cam footage following a serious collision on the M25 in Watford.
At around 7pm on Saturday, November 21, three vehicles were involved in a serious collision close to junction 20.
The vehicles involved were a red Fiat, a silver Toyota Corolla and a black BMW.
The driver of the Fiat, a woman, sustained a serious head injury. She remains in hospital in a serious condition.
Sergeant Russ Jones, from the Bedfordshire, Hertfordshire and Cambridgeshire Road Policing Unit, said: “Our thoughts are with the injured lady and we very much hope that she recovers well. I am appealing for anyone who saw what happened to get in touch.
“Were you driving in the area? Did you see the collision? Or did you see the events leading up to it? Anything you can tell us could be really important for the investigation.
“Similarly, if you were driving in the area and have a dash cam fitted to your vehicle please do check it and let us know if you spot anything that could be significant.
“If you saw what happened, have useful dash cam footage, or simply have information about the incident, please call the non-emergency number 101 or email me at email@example.com quoting ISR 619 of 21 November.”